The present invention is directed to a method and apparatus for improving the accuracy of positive feed cording in manufacturing cord reinforced articles. Specifically, the disclosed method and apparatus provide instantaneous measurement of cord properties when feeding the cord to a rotating drum during the manufacture of articles such as belts, hoses, tires, reinforced airsleeves, and other similar articles formed in a tubular fashion during manufacturing.
Cord feeding occurs during the manufacture of many reinforced articles, such as power transmission products. One example of a positive feed cording system is described in WO 97/22461.
The positive feed cording system includes means of metering a controlled length of cord onto a rotating drum in a helical pattern. The system uses a powered drum with an encoder to meter the cord that passes over it. The ratio of drum rotation to cord length applied is determined by the accurately known drum diameter (or more precisely, the circumference) and by the radial distance from the drum surface to the neutral bending plane of the cord; the last distance being the effective pitch line differential (EPLD).
The EPLD is not easily measured by examination of the cord, even if it is placed on a capstan. The average EPLD can be determined empirically by measuring the pitch length of the finished manufactured product, but accuracy is limited by other factors contributing to belt pitch length. The EPLD depends in part on the tension used, so each cord must be empirically tested at each tension to be used. Lot to lot variations in cord modulus, diameter, or resistance to flattening affect the actual EPLD, so the metered length of cord per capstan revolution is more accurately determined by the instantaneous value of the EPLD.
The EPLD is typically determined by a separate test performed prior to building the article on a rotating drum. The test consists of winding cord from the metering drum onto a rigid drum. The circumference of the rigid drum is accurately known and different from that of the metering drum. During the test, the rotation of both drums is accurately measured and the EPLD calculated from their relative velocity or displacements. This value is used to calibrate the building machine when that cord is later applied to a product slab being corded. This test can be repeated with sample of a material from several lots to determine the average and standard deviation of the EPLD property. Likewise, a cord material can be run under different conditions (i.e. cording speed, tension, temperature, and relative humidity) to determine the sensitivity of the EPLD of that cord to operating conditions.
However, the test conditions can often differ from the actual operating conditions and thus the predetermined EPLD may not be accurate at the time of building. Additionally, the EPLD can vary from material lot to material lot, requiring a choice of either frequent pretesting of each material lot or using an average, and possibly, inaccurate, EPLD for each material lot.
Accurate cord length is of particular importance in making toothed timing belts since an error in cord length can result in improper meshing of teeth and premature tooth or belt failure.
The present invention is directed to a method and apparatus for improving the accuracy and ease of use for positive feed cording by employing a continuous and automatic evaluation of the EPLD of the cord. It provides a more accurate EPLD and is tolerant of variations in the cord properties.
The disclosed apparatus is directed toward an apparatus for accurately applying a cord to a rotatable mandrel to produce an intermediate article of manufacture. The apparatus includes a rotating build mandrel, a cord supply, and a feed capstan for assisting in feeding cord from the cord supply to the mandrel along a defined cord path. In addition to these elements, the apparatus includes at least two additional drums located in the cord path. The drums have different diameters. Encoders are connected to each drum for measuring at least the angular movement of the drum. Control means are used to determine the effective pitch line differential of the cord as the cord travels through the cord path from the measured angular movements of the drums.
In another aspect of the disclosed apparatus, one of the drums is power driven to drive the cord along its cord path.
In another aspect of the disclosed apparatus, one of the drums measures the cord tension as the cord travels over the drum.
In another aspect of the disclosed apparatus, two additional drums are located in the cord path. The drums have diameters different from each other, but may be identical to the first two drums in the system about which the cord already travels. Encoders are connected to each of the two additional drums. The encoder measures at least the angular movement of the drum.
In another aspect of the invention, the tension T1 in the cord path as the cord travels over the first two drums differs from the tension T2 in the cord path as the cord travels over the two additional drums.
In a further aspect of the invention, the controls means measures the cord modulus in accordance with the following equation:
modulus=xcex94T/(xcex94L/original cord length)
where xcex94T=the absolute difference between T1 and T2 and xcex94L is the absolute value of the change in the cord length measured between the first set of drums and the two additional drums.
Also disclosed is a method of applying a cord to a rotatable build mandrel. The method includes supplying a cord, feeding the cord along a defined cord path, and winding the cord onto a rotatable mandrel to build an intermediate article of manufacture. In accordance with the invention, prior to winding the cord onto the rotatable mandrel, the cord is passed over two drums of differing diameters. As the cord passes over the drum, the angular movement of the drum is measured. From the measurement of the angular movement, the EPLD of the cord is calculated. The equation to measure the EPLD is:   EPLD  =                    (                  RL          *          AL                )            -              (                  RS          *          AS                )                    (              AS        -        AL            )      
where R is the radius of each drum, A is the angular displacement, L represents the larger drum, and s represents the smaller drum.
In one aspect of the method, the cord is wrapped about a drum that is motor driven.
In another aspect of the method, the tension of the cord is measured as the cord passes over one of the drums.
In accordance with another aspect of the invention, the cord passes over two additional drums. The drums have differing diameters from each other and may or may not be of identical diameters as the first two drums. Preferably, the tension at which the cords travel over the two additional drums is different than the tension at which the cord travels over the first two drums. The cord modulus is measured in accordance with the following equation:
modulus=xcex94T/(xcex94L/original cord length)
where xcex94T=the absolute difference between T1 and T2 and xcex94L is the absolute value of the change in the cord length measured between the first set of drums and the two additional drums.